Various different forms of vertical windmills heretofore have been designed and provided with wind-shielding structure and other features such as those included on the windmill of the instant invention. Examples of these previously known forms of vertical axis windmills are disclosed in U.S. Pat. Nos. 204,404, 1,096,057, 1,640,296, 1,687,181, 1,974,008, 4,031,405, 4,134,707, 4,237,384, 4,245,958 and 4,278,896.
However, most of these previously known forms of vertical axis windmills include complex controls for wind-shielding portions thereof which do not perform the dual function of wind-shielding at high wind velocities as well as wind flow concentrating at lower wind velocities.
Accordingly, a need exists for a simplified vertical axis windmill with automatic wind-shielding structure to prevent rotor overspeeding at high wind velocities and wherein the wind-shielding structure additionally includes wind concentrating means automatically operable at low wind velocities to deflect additional wind into the sweep area of the rotor of the windmill.